1. Field of the Invention
The invention relates to a pipe-welding apparatus and more particularly to a pipe-welding apparatus with a centering device for centering the pipe-welding apparatus relative to a pipe which is to be welded to an end-plate, which device is provided with a tubular center part arranged to interact with a spindle of the pipe-welding apparatus, which spindle can be introduced into the center part, with two pairs of sleeves supported by the center part and arranged axially next to one another, the one sleeve in each pair being rigidly connected to the center part and the other sleeve being slidingly displaced along the center part, and with a number of balls located between the sleeves in each pair of sleeves and arranged to interact yielding with the mutually facing end surfaces of the pair of sleeves, the axial separation of which increases in the direction toward the periphery of the device.
2. Background Information
In U.S. Pat. No. 4,142,084, a welding apparatus with a centering device is described, in which two ball races interact with conical surfaces of two sleeves arranged on a pipe, the ball races moreover being separated by a floating ring arranged between them, which can take up an inclined position in relation to the radical plane of the device. The aim of this somewhat complicated arrangement is to make possible the use of the centering device in pipes with slightly oval cross-section. The balls are held in place in the device by ball holders with circular openings, the diameter of which is slightly smaller than the diameter of the balls. When the device is introduced into a pipe, the balls are pressed against certain parts of the edges of the opening, which are thus subjected to rapid wear. The openings are deformed and gradually become so large that the balls fall out. Constructing the device is complicated and mounting the balls is laborious. In general, the pipes which are to be welded are sufficiently cylindrical and special constructional measures for adapting the centering device to slightly oval pipes is not necessary.